With the improvements of industry technologies and the trend of low-quantity highly diversified products, the key to taking the lead among competitors and expanding market is on shrinking manufacturing time of products, which has become an important subject in product development. Thereby, people take related reverse engineering technologies more and more seriously. Product examinations, industrial fabrications, product shape designs, object profile scans, and multimedia animation productions all count on a measurement technology with rapidity and precision. In addition, the most important thing to implement reverse engineering is measurement capability.
Traditional automatic metrology technologies can be divided into two categories: contact metrology and non-contact metrology. Non-contact metrology uses light as the measurement tool and is applied extensively. In general, a grey-scale grating is projected to a workpiece under measurement for grating projection measuring method. However, because of disturbance from background light and shadow, the workpiece under measurement is inconspicuous, and consequently the stripes will be judged erroneously. If the surface of the workpiece under measurement is too glossy, one part of the surface of the workpiece under measurement will reflect strongly to make other stripes look unclear or break. Furthermore, if abruptly ascending or descending curves exist on the workpiece under measurement, shadows are easy to result and will be judged erroneously as stripes. In such a circumstance, stripe crossing happens.
In addition, traditional automatic metrology technologies still have the following drawbacks of:                1. Difficulty in identification with single-color gratings. Referring to FIG. 7, in traditional monochromatic stripes emitted on the workpiece under measurement, if the surface of the workpiece under measurement is clear, the moire method of phase-shift scanning can reconstruct three-dimensional model of the workpiece under measurement completely using high-speed, high-resolution photographic apparatus to extract grating images. However, as shown in FIG. 11 and FIG. 12, when the grating is projected on rough surface of the workpiece under measurement, the grating stripes twist and deform. If part of the stripes is covered by the shadows of the object, it is difficult to judge the correspondence of stripes, and consequently will affect reconstruction of images.        2. Unavailability of switchable picture-in-picture on displays. In tradition optical metrology, the grating of the projection apparatus and the extracted grating image by the photographic apparatus are displayed by two displays and thereby cannot be displayed on a single frame, which causes numerous equipments, complex controls, and difficult inspection. Besides, viewing images and adjusting focus of the photographic apparatus are two separate actions. It is not possible to adjust the photographic apparatus directly form the display when viewing images, causing great inconveniences.        3. Being unable to adjust gratings. Most of the gratings in the prior art are designed fixed. The stripe density and contrast cannot be adjusted. Thereby, accuracy will be lost for measurement on a small workpiece.        
Accordingly, it is necessary to develop a new technology for solving the drawbacks described above.